Electron transport systems of axenic Entamoeba histolytica will be investigated beginning with amebal flavins and amebal ferredoxin and continuing to elucidate activities of amebal flavoenzymes and high molecular weight iron-sulfur proteins. In another direction the mechanism for formation of amebal nucleic acids will be explored including the source of the ribose moiety and the nucleotide bases. It is our hypothesis that the subjection of this organism, essentially anaerobic, to the more aerobic conditions of tissue and intestinal epithelium in some manner triggers its pathogenicity.